Method of preserving latex and product thereof



Patented Oct. 16, 1945 METHOD OF PRESERVING LATEX AND PRODUCT THEREOFWilliam D. Stewart, Akron, Ohio, assignor to The B. F. Goodrich Company,New York, N. Y., a

corporation of New York No Drawing. Application October 27, 1943, SerialNo. 507,870

4 Claims.

This invention relates to a method of preserving latex, particularlyfresh latex, and to the product thereof.

Latex that has been freshly-collected from the rubber trees containsenzymesthat, together with the bacteria picked up in handling the latex,cause the latex to putrefy and coagulate within a relatively short time.Various methods of preserving the latex have been proposed in the past,such as the ammonia treatment now commonly used, but all these have beenonly generally eiiective and all have been more or less unsatisfactory.

I have discovered a method of treating latex, particularlyfreshly-collected latex, to produce a sterile, stable product capable ofbeing stored for long periods of time without putrefaction orcoagulation. By the method of this invention the pH of the latex isadjusted to a value of from 9.8 to 10.0 and then there is added a smallproportion of a member or members of the class consisting of those azodyes, nitroso dyes, and triphenyl methane dyes having a solubility ofnot less than about 0.01%, by weight, in the alkaline latex. In the caseof the preferred freshly-collected latex it should be treated within notmore than eighteen hours after being collected from the rubber tree. ThepH of the latex can be adjusted by adding a buffer solution, alkali,alkaline salt, ammonia, or the like, to the latex until the pH reachesthe specified range. Then the dye is added. Examples of dyes that may beused in this invention include gentian violet, crystal violet,acriflavine, flavine, basic fuchsin, thionin, corallin yellow, toluidineblue, dahlia, malachite green, methyl green, pararosaniline, methylviolet, methylene violet, and the like. These dyes, and others ofsimilar nature, may be used either alone or in combination to make theimproved preserved latex of this invention. The dyes may be used in anydesired proportion but usually should be employed in amounts rangingfrom about 0.01% to about 0.20% by weight of the latex. They may beadded either before or after the pH of the latex has been adjusted tothe specified range and, if necessary, the pH may be readjusted afteraddition of the dye or dyes to bring the pH back Within the range of 9.8to 10.0.

Ammonia is the preferred material for use in adjusting the pH of thelatex as it is easy to use, can be easily removed from the latex, anddoes not unduly complicate compounding of the latex. When the preferredfreshly-collected latex is preserved the usual amount of ammonia will befrom about 0.25% to 0.35% by weight of the latex. In this invention theammonia, or other material, is

insufiicient alone to preserve the latex but the combination with thedye does produce a latex that remains sweet and pure for long periods.

In a specific example of this invention ammonia is added tofreshly-collected latex until the pH is raised to 10.0 and immediatelythereafter 0.09% of gentian violet by weight of the latex is added tothe latex. This produces a latex that will remain sweet and uncoagulatedfor long periods of time.

I have found through numerous experiments that raising the pH of thelatex to within the relatively narrow range of 9.8 to 10.0 and thentreating the latex with one or more of the dyes disclosed hereinproduces a preserved latex that Will remain sweet and unchanged overlong periods of time with no danger of coagulation and putrefaction. Thedyes can also serve a dual purpose in that a preserved and colored latexmay be prepared in one operation by the choice of a dye to give anydesired color from among the group of dyes disclosed herein. This methodof preserving latex is likewise applicable to preserving latex that isnot freshly-collected but that has been preserved by other meansalthough the method is more specific to the preservation offreshly-collected latex.

A will be apparent from the foregoing the preserved latex preparedaccording to this invention ordinarily will contain only the naturallatex itself and the ammonia or other material added in adjusting the pHtogether with the azo dyes, the nitroso dyes, and the triphenyl methanedyes as described. Any of the usual compounding or conditioning agentsmay later be added as desired to prepare the latex for specific uses butsuch materials preferably are not added at the plantation.

This application is a continuation-in-part of my copending applicationSerial No. 371,200, filed December 21, 1940.

Having disclosed my invention it is my desire to protect it broadlywithin the spirit and scope of the invention as set out in the appendedclaims.

I claim:

1. The method of preserving freshly-collected latex which comprisestreating the said latex within about eighteen hours after its collectionfrom the tree by adding to the said latex a quantity of alkalinematerial equivalent to from about 0.25% to 0.35% ammonia by Weight ofthe latex, said quantity being insufiicient alone to preserve the latex,and also adding from about 0.01% to about 0.20% by weight of the latexof a dye selected from the class consisting of the azo dyes, the nitrosodyes and the triphenyl methane dyes,

said dye being soluble in the alkaline latex to the extent of at leastapproximately 0.01% by weight.

2. The method of preserving freshly-collected latex which comprisestreating the said latex within about eighteen hours after its collectionfrom the tree by adding to the said latex not more than about (1.35% byweight of ammonia together with not more than about 0.20% by weight of adye selected from the class consisting of the azo dyes, the nitroso dyesand the triphenyl methane dyes, said dye being soluble in the ammoniatedlatex to the extent of at least approximately 0.01% by weight.

3. Preserved latex prepared in accordance with the method of claim 1.

4. Preserved latex prepared in, accordance with the method of claim 2.

WILLIAM D. STEWART.

